Thermographic copying process



United States Patent O1F U.S. Cl. 96-27 13 Claims ABSTRACT OF THE DISCLOSURE Multiple copies of a printed original are made by a repetitive process involving radiation heating at image areas of a master sheet coated with a non-tacky Vaporizable solid, condensing the vapor at corresponding areas of a receptor sheet as a metastable liquid, and powder developing the liquid image.

This application is a continuation-in-part of copending application Ser. No. 189,029 iiled Apr. 20, 1962, now abandoned.

This invention rela-tes to the copying of graphic originals. It has particular reference to a novel process for the preparation of multiple copies on plain untreated paper, involving the transfer to the paper of latent-imageforming material by a heat-pattern developed in a radiation-absorptive image on the original or on an imaged master sheet, for example on a printed master or on an intermediate master formed-from the graphic original by a thermographic or tr-ansfer process or through the agency of actinic light.

In one aspect the invention is useful in making possible the rapid and economical direct duplication of printed, e.g. typed or handwritten, or other graphic intelligence. In another aspect the invention is useful in providing multiple copies of printed originals such as books, drawings, sketches, etc., which, because printed on heavy or stiff backings or in various colors, are ditlicult to copy by customary thermographic copying procedures Iand accordingly have required much more complicated and expensive photographic or like copying processes. The invention permits the preparation of large numbers of copies at a rapid rate, on plain paper, and without the necessity of development with lchemical solutions or vapors as required in photographic processes.

Prior art copying procedures are known in which a latent electrostatic image of an original is rst produced on a photoconductive sensitive plate, the image is developed with a thermoplastic ink powder, and the powder image is then transferred to a plain paper receptor and ixed by heating. Complicated and expensive machines and apparatus are required in order to achieve the desired exposure and to convert the latent image into a visible copy. High voltages are required in electrostatically charging the sensitive plate, and are lhelpful in reducing darkening of the background in the finished copy, but involve danger and 'annoyance to personnel as well as considerable expense. Block areas frequently reproduce only in outline.

Another copying method which has been suggested for making multiple copies involves lightly coa-ting the `surface of the graphic orginal with an oily liquid which is then removed 'at image areas to an Iadjacent paper receptor sheet on irradiating the original with intense infra-red radiation. The oily latent image produced on the paper receptor is later made visible by much the same process used in the detection of finger-prints, i.e. by the application of colored very nely divided dusts or powders which cling selectively to the oily areas and which may then be fused in place. The powders have a tendency to be re- 3,446,617 Patented May 27, 1969 ICC tained by much of the background area, in part because of -contact transfer of the oily iluid at these unheated areas. The Isupply of oil must be replenished for making each successive copy. Since the oil is applied directly to the original, only those printed documents or the like which are unharmed by such oils or which are expendable may safely be copied by this method. Uniform 'application of the oil requires special machinery, which prohibits the application of the process to many originals. The process, because of the nature of the radiation employed, is restricted as to the type of printed original which may be copied. With normally solid waxy or resinous materials in place of liquid oils there is obtained either extremely faint or incomplete imaging, or a very few dense copies having ysevere backgrounding.

The present process, on the other h-and, is applicable to the copying of any graphic original having` visibly distinct image land background areas. In accordance with one preferred embodiment, a light-sensitive lm is first exposed to light While in contact with the original, and the lm is then heated in contact with a reactarnt-coated intermediate master sheet on which the image is thereby reproduced. The resulting master is then irradiated in con-tact with plain paper to form thereon a latent image which is promptly rendered permanently visible. The latter process is repeated to provide 4any desired number of copies. The process involves no treatment with liquids or vapors as is required of other photographic or like processes, but instead employs radiant or conducted energy, in the form of radiation or heat, in producing both the intermediate master and the nal copies.

In the drawing, which is not necessarily drawn to scale,

FIGURES 1 and 2 illustrate in schematic cross-section the preparation of an intermediate master from a graphic original;

FIGURES 3 and 4 rsimilarly illustrate the formation of a latent image and development of a visible image using an intermediate master prepared as in FIGURES l and 2;

FIGURES 5 and 6 illustrate the preparation of a latent image using a different and unitaryk form of mas-ter; and

FIGURE A7 illustra-tes a graphic original which serves also as a master.

In FIGURE 1 a light-sensitive transparent film product 10 consisting of a transparent lm support 11 carrying a light-sensitive reactant coating 12 is placed upon the printed surface of a graphic original 13 consisting of a heavy white paper 14 printed with visible image areas 15, and the composite is irradiated with actinic light indicated by broken arrows 16. Irradiation is continued until the portions ofthe reactant layer 12 lying above the rellective background areas of the original are substantially completely desensitized, the portions 22 above the lightabsorptive printed areas 15 remaining at least partially sensitive. The lm 10 is then removed and placed in conltact with an intermediate master sheet 17 a-s in FIGURE 2. Sheet 17 consists of a paper base 1S coated on one surface with an image-forming co-reactant layer 19 and on the other with a hard and non-tacky transfer layer 20. Heat, indicated by wavy arrows 21, is conducted to the composite and permits the transfer of residual reactant from the still sensitive image areas 22 of the layer 12 to lcorresponding `areas 23 of co-reactant coating 19, where reaction to a visible and infra-red-absorbing reaction product occurs. The intermediate master sheet 17 is now ready for use in forming multiple latent images.

In preparing the latent image copies, the intermediate master 17, now carrying the visible image 23 in the imagelforming layer 19, is placed with its transfer coating 20 against a `sheet of plain paper 24 and subjected to radiation rich in infra-red, indicated in FIGURE 3 by arrows 25. The heat-pattern developed in the infra-red-absorptive image areas 23 is conducted through the sheet 17 as indicated by wavy lines 26 and causes transfer of minute portions of layer 20 to the surface of paper 24 in a pattern corresponding to that of the intermediate image 23 and here represented as lightly dotted areas 27. Since the transferred material remains essentially invisible until development, it is appropriately designated as forming a. latent image.

The latent image is promptly developed into a permanent visible image in accordance with procedures indicated in FIGURE 4. The surface of the imaged sheet 24 is covered with a layer of colored thermoplastic developing powder 28 which adheres at the latent image areas but is removed from the background areas by simple shaking or blowing. Heat, represented by wavy arrows 29 is then lapplied-or may be generated in a radiation-absorptive powder by exposure to suitable radiationto -fuse the thermoplastic powder or otherwise to provide a permanent visible image.

The process as described in connection with FIGURES 3 and 4 is repeated using additional sheets of plain paper 24 to provide any desired number of copies.

In making the light-sensitive coating 12 of the sheet of FIGURE 1 there may be employed any of a wide variety of sensitive reactant materials or combinations of materials which are normally capable of rapidly reacting, under the conditions provided, with the co-reactant of the coating 19 of the intermediate sheet 17 of FIGURE 2 to provide an infra-red-absorptive reaction product and which sensitive reactant materials at the same time are capable of being desensitized against such reaction by exposure to actinic radiation, i.e. to visible or ultraviolet light. The sensitive reactant materials are preferably releasably retained on the surface of a thin transparent polymeric supporting film by means of a small proportion of polymeric or resinous binder. The mixture is conveniently applied from solution or suspension in a volatile liquid vehicle which is then removed by evaporation, the entire operation being conducted in the absence of any excessive amount of actinic radiation. The sensitive reactant material may alternatively be incorporated in a light-transmissive porous fibrous web inthe substantial absence of added binder.

On the `same basis there may be employed as the coreactant material of the image-forming coating 19 of intermediate master sheet 17 any material or combination of materials normally capable of rapidly reacting with the light-sensitive reactaut material of coating 12 to provide visibly distinct and preferentially infra-red-absorptive image areas. The two-sheet composite, with coatings 12 and 19 in contiguity, provides in effect a form of heatsensitive copy-sheet as used in well-known thermographic copying processes, ywhich in this instance is also lightdesensitizable.

The functions of the sensitive `sheet 10 and intermediate sheet 17 of FIGURES 1 and 2 are combined in the structures and process illustrated in FIGURES 5 and 6. The unitary sheet 30 comprises -a thin transparent supporting web 31 having a first coat 32 containing an image-forming co-reactant as in the coating 19 of FIGURE 2, and a second coat 33 containing the desensitizable reactant of coating 12 of FIGURE 1 as well as the transferable ingredient of coating of FIGURE 2. The sheet is first placed with its coated surface in contact with the printed surface of a graphic original 34 having light-a-bsorptive inked image areas 35 on a reflective white paper background. The printed surface is irradiated, with actinic light 36 applied through the light-transmissive sheet 30 to an extent just sufficient to provide complete desensitization 1at background areas, the coating 33 retaining a diminished but still adequate degree of sensitivity or potential reactivity at image areas. The `sheet 30 is then heated to cause reaction at the sensitive areas and form visible infra-red-absorptive image areas 37 as shown in FIGURE 6. Irradiation through the transparent web 31 4 of the sheet 30 with infra-red radiation 38 while the coated surface is in contact with plain paper 39 then produces on the latter a latent image 40 which is promptly developed with a heat-softenable colored developer powder and fixed by heating, as described in connection with FIGURE 4.

The same infra-red-absonptive image may be produced in the sensitive image layer of the unitary sheet 30 by the thermographic copyin-g process either by frontprinting or by back-printing. In the former process, brief exposure to intense infra-red radiation in place of the actinic radiation 36 provides a heat-pattern on the graphic original 34 and results in the formation, by chemical reaction, of image areas 37. The background areas may then be desensitized by exposing the sheet to actinic radiation.

The sheet 41 of FIGURE 7 includes a thin dense paperlike web 42 having on one surface a coating 43 of transferable latent-image-producing material as defined in connection with coating 20 of FIGURE 2, and on the other surface a selectively radiation-absorptive image pattern in the form of printed or hand-written indicia 44. Such a product may be made by printing onto a pre-coated sheet or by coating a previously prepared graphic original.

Various other combinations and modifications are contemplated, particularly with respect to the absorptiveimage-forming transfer sheet, since any differentially radiation-absorptive copy capable on irradiation of producing the required heat-image to cause transfer of the desired latent image is equally effective. Thus in the structure illustrated in FIGURE 2 as sheet 17, the coating 19 may for example be a photosensitive silver halide-gelatin emulsion layer which is exposed to a light-image and chemically developed and fixed to provide an infra-redabsorptive image pattern. In all cases the transfer layer is stable and inactive during handling, storage and shipping, yet is immediately and effectively fractionally transferred to form readily developable latent images when locally briefly heated in contact with plain paper or other suitable collecting surfaces as herein described and illustrated.

Surprisingly, it has now been found that certain hard and completely non-tacky fusible solid materials, when applied in exceedingly small amounts to paper-like or other suitable supporting media by fractional heat-transfer from an imaged coated intermediate master or other source sheet as hereinbefore described, become temporarily capable of retaining the image-forming dusts or powders. It has further been found that the use of these materials and master sheets makes possible the production of large numbers of copies from a single coated master. The coated master sheet is free of oily, greasy or sticky characteristics and instead forms a clean, convenient, stable article of commerce which can be packed, stored, and used without soiling of surfaces or articles with which it comes in Contact.

These and other novel and advantageous results are obtained, in accordance with the present invention, by employing as the transfer component, of which the latent image is produced, a normally hard solid and non-tacky material melting within the approximate range of 70- 170 C., capable of vaporizing at elevated temperatures of the order of C. as attained in the thermographic copying process, and in particular possessing a strong tendency to form a supercooled melt, i.e. to remain temporarily as a fluid metastable liquid at normal room temperature, on being thus vaporized and transferred in minute quantities to a receptor surface.

Due to the lack in the available chemical literature of adequate data for defining the latent image-forming materials useful in the practice of the invention, it has been found necessary to establish certain definitive test procedures which will now be described.

The melting point or melting range of the material may be determined, for the purposes of this invention, by

solidication, when it occurs, may be detected by attempting to smear the droplets with a spatula. The solidied droplets remain unchanged; liquid droplets are altered in shape and will frequently rapidly crystallize when thus manipulated.

The application of the test procedures just described to typical candidate materials for determining their possible utility in providing stable non-tacky latent-imageproducing copy-sheet matsers will now be illustrated in terms of the tabulated results obtained from such tests.

Prelim. Test Sens. Test Material M.P. Xtal.' Fog Soilidn Result Santieizer 9 105-110 RT 30+ Excellent copies. Aroclor 1268 135-176 RT- 30+ Do. Benzotriazole... 97 23 10+ Do. 2,4-dihydroxy benzophenone.. 147 RT- 30+ Do. Tribenzylamine 94 RT 10+ Very good copies.

enzil 94-96 RT- -I- 30+ Excellent copies. Vanillin 82 21 10 Very good copies. Benzoin 135-136 30 10+ Excellent copies. Phthalophenone 114-115 RT- 10+ Very good copies.

P 48-49 RT- 10+ Weak image; bkgd.

Stearic acid 54- 50 0 N o image. Phloroglucinol 216-220 180 O Do. Acetamide 80-82 39 (15 see.) Backgrounding. Methyl red 160-178 x 0 Red stain. Adipic acid 152-153 140 y 0 No image. o-Nitrobenzaldehyde 39-42 RT- 10+ Unstable; bkgd. Carnauba wax... 90-100 x x No image. Carbowax 200 (liq.) x x Backgrounding. Piceolite S135 118-132 x x Partial image; bkgd. Oil in wax 90 x (i) x x of cold water is used for both determinations. After the stage has been heated above the melting point of the sample, it is cooled and the temperature noted at which crystallization or solidification occurs. Both heating and cooling may be accomplished at somewhat higher rates of temperature change than are ordinarily specied where more precise measurements are required. Materials which when thus treated remain liquid to a temperature well below their melting points are ordinarily found to be effective; materials which crystallize or solidify at or near their melting points cannot ordinarily be used for making powder-retaining latent images in accordance with this invention. Some materials solidify to a glassy rather than a visibly crystalline state, a condition which is easily determined by applying moderate pressure on the coverglass with a spatula; glassy droplets retain their shape, whereas the liquid droplets flow or rapidly crystallize.

A somewhat more sensitive test for supercooling is conveniently made in conjunction with the test for volatilization. In this test a metal base, such as the metal plate of a Fisher-Johns melting point apparatus, is heated to the desired temperature, e.g. 150 C. A cover-glass is placed on the base and a few small particles of the material to be tested are sprinkled on the glass. A second cover-glass, initially at approximately room temperature, is suspended over the sample parallel to the lower glass and at a distance of approximately one-eighth inch. The upper glass may less accurately be held with hand-operated clamp or tweezers, or may be supported on parallel glass rods laid across opposite sides of the lower cover-glass, or for accurate positioning may be attached to a simple hinge mechanism having a micrometer adjustment. The appearance on the under surface of the upper cover-glass, as seen -through the glass, of a visible haze or fog of droplets or particles of condensate within about one-half minute after rst placing the glass in position indicates adequate vaporizability.

The cover-glass containing the fog droplets is then carefully removed to a microscope and further observed. In some instances crystallization occurs during transfer of the sample; in others the effect is noted after a feW seconds. With materials suitable for the purposes of the present invention, crystallization or solidication occurs only after at least about one-half minute, the preferred materials requiring at least ten minutes. Non-crystalline Santicizer 9 is a mixture of orthoand para-toluene sulfonamides melting at about C. The melt remains liquid when first cooled to or somewhat below room temperature. The material vaporizes at C. to produce a visible haze in the fog test and the droplets on the glass plate remain liquid for at least 30 minutes at room temperature. This material provides a stable non-tacky thin coating on paper and is fractionally transferred at heated areas to form latent image areas which are effectively developed with colored powders all as hereinbefore described, providing a large number of excellent copies.

Aroclor 1268 is a solid chlorinated diphenyl having a normal specilic gravity of 1.646-1.653 and a vapor pressure of 760 mm. Hg at about 435 C. It meets the requirements of the fog test and the test for metastability at room temperature, and provides excellent copies.

Benzotriazole, melting at 97 C., is found to crystallize on cooling to 23 C. in the mass crystallization test, but when vapor transferred in the fog test the droplets remain liquid for at least l0 minutes. The material provides excellent copies by powder development of the latent image.

Triphenylphosphate (TPP) melts at well below 70 C. and as a transfer coating in the reproduction process here described is found to transfer at background as well as image areas, resulting in darkening or smudging of the background during image development.

Stearic acid melts at 5457 C. and solidiiies within a few degrees of the melting temperature; and the condensed droplets obtained in the fog test are found to solidify immediately. No developable latent image is obtained with this material.

Acetamide solidies within 15 seconds in condensed droplet form in the fog test and, like stearic acid, does not yield a developable latent image.

Methyl red (p-dimethylaminoazobenzene-o-carboxylic acid) forms a glass during cooling in the melting point test. It transfers in the fog test but solidies on transfer and does not produce a developable latent image.

Othro-nitrobenzaldehyde melts at about 40 C. and vaporizes so readily at low temperatures as to possess undesirable instability in the form of thin coatings. Any image formation is accompanied by heavy backgrounding.

Carnauba wax solidies without visible crystallization during cooling under the microscope. It produces no visible condensate in the fog test and no developable latent image in the copy process here described.

Carbowax 200 is a normally liquid water-soluble waxy polyethylene glycol which transfers excessively at both image and back-ground areas.

Piccolyte S-135 neutral thermoplastic terpene resin melts at 11S-132 C. and solidiies without apparent crystallization on cooling. It produces no visible condensate in the fog test. One or two vague and indistinct powderdeveloped copies may be produced on plain paper by thermographic reproduction with a master sheet coated with this material, apparently due to adherent mass transfer of the resin, but the copies are heavily backgrounded and completely ineffective.

A homogeneous blend of parts of HB-40 mineral oil and 90 parts of carnauba wax melting at about 90 C. when heated at 150 C. in the fog test forms a visible deposit during the first few moments of heating but on continued heating fails to produce further fogging on additional test plates; whereas materials such as benzil, having approximately the same melting point, continue to deposit a visible fog on successively applied plates until the entire sample is exhausted.

From the foregoing it will be apparent that the rst nine materials tabulated meet the requirements as to melting point, volatilizability or vaporizability, and ability to supercool to a fluid metastable liquid state, and are capable of forming stable coatings which can be fractionally transferred by localized brief heating in thermographic copying processes in the form of powder-developable latent images. It will also be apparent that the remainder of the materials tabulated either lie outside the range of melting-points applicable in the thermographic process, or are excessively or inadequately volatile, or crystallize or solidify on cooling below their melting point without assuming a fluid metastable liquid condition, or fail to remain in the metastable condition for a sufcient time; and therefore that these materials produce unstable coatings or coatings which do not selectively transfer or which transfer excessively or which when transferred are ineffective under the conditions and for the purposes here contemplated.

The following illustrative but non-limitative examples will provide for a further understanding of the invention.

Example 1 A transparent transfer sheet is rst prepared by coating thin transparent Mylar polyester lm with a solution of 0.2 part lby weight of 4-methoxy-l-naphthol, 0.088 part of erythrosin and l0 parts of ethyl cellulose in 90 parts of methyl ethyl ketone, applied through a coating orice of 3 mils (0.003 inch), and dried in total darkness.

An intermediate master sheet is prepared by coating one surface of 25 lb. map overlay tracing paper with a ball-milled mixture of l0 parts of silver behenate, one part phthalazinone, 3 parts of poly-t-butylmethacrylate and 86 parts of acetone, applied at an orifice of 3 mils and dried. The reverse side of the paper is then coated with a 20% solution of Aroclor 1268 in acetone, lightly applied as uniformly and rapidly as possible with a cotton swab, and the sheet is again dried. The dry coating has a Weight of about 0.6-0.7 gram/sq. ft. The dried Aroclor coated surface is found to be completely non-receptive of developing powder such as carbon black.

The pink colored transparent transfer sheet is placed over a graphic original typewritten on white paper and with the coated surface of the transfer sheet in close uniform contact with the typewritten surface of the original.' The composite is illuminated with intense visible light from a bank of tungsten lament lamps and through the transfer sheet for a time, typically within the approximate range of to 30 seconds, just sufficient to cause essentially complete desensitization at areas of the transfer sheet corresponding to the background areas of the printed original.

The thus reflex-exposed transfer sheet is next placed with the coated surface in contact with the silver soap coating of the intermediate master sheet and the composite is subjected to uniform elevated temperature, preferably under pressure contact with an infra-red absorptive black paper carrier sheet which is then heated by being briefly exposed to intense radiation rich in infrared, e.g. by means of commercial thermocopying equipment. Heat may alternatively be Supplied by means of heated platens or rollers, or in other ways. A copy of the original typewritten image in the form of black letters on a white background is formed on the coated intermediate master sheet. The depleted transfer sheet is discarded.

The master sheet is next placed with the coated reverse surface in contact with a sheet of plain untreated white paper and the composite is passed through the thermocopying machine, with `brief intense irradiation of the imaged surface. The plain paper is removed and is lightly dusted with carbon black over the surface contacting the master sheet. The black powder is found to adhere well at areas corresponding to the image areas of the original, resulting in readable copy which however smudges badly in handling. Carbon black has a tendency to cling to untreated paper, and the background areas of the copy are found to be irregularly smudged and dirtied.

Additional copies are prepared from the same master sheet in the same manner, a total of up to readable copies being easily obtained.

Copies having much improved clarity of background are obtained by substituting for the carbon black a developer powder consisting of very fine substantially spherical pellets of colored thermoplastic resin. Phenolic, polyterpene, polyester, aryl sulfonamide, polyphenyl, and epoxy synthetic resins, as well as rosin and other natural gums and resins, are useful. They may be colored with various colored pigments; for example, resins pigmented with carbon black, Prussian blue, or toluidine red are useful for this purpose. As a specific example, a mixture of 15 parts by weight of carbon black, 240 parts of Santolite MHP aryl sulfonamide formaldehyde resin, and 60 parts of Bakelite CKR 5360 phenolic resin, mixed in liquid form until homogeneous and then cooled and ground to 100 mesh, produces excellent images and leaves an unsmudged background when applied as above described and fixed by heating at about C. Polyethylene micro-beads or pellets loaded with carbon black are particularly suitable. The pellets adhere well to the metastable liquid latent image areas but are easily and completely removed from the background areas by simple shaking or snapping of the sheet or by means of an air blast. The copy is rendered permanent by brief heating, e.g. in an oven or, for infra-red-absorptive colors, by exposure to infra-red radiation at an intensity sufficient to fuse the thermoplastic resin to the paper surface.

Example 2 A sheet of vellum, a semi-transparent thin dense paperlike product commonly used by draftsmen in making engineering drawings, is coated on the back surface with a thin layer, applied as uniformly as possible with a cotton swab, of a 20% solution of Santicizer 9 in acetone, and the sheet is well dried. The dry coating weight is about 0.6-0.7 gram/sq. ft. The coated sheet is non-tacky and can be handled, stacked or led, and stored Without blocking and without harm to contacting surfaces. It does not retain developer powders dusted over the coated surface.

Pencil markings, e.g. in the form of an engineering drawing, are then inscribed on the face or marking surface of the vellum. The sheet is placed with its coated back surface against a sheet of plain paper and the printed front surface is briefly exposed to intense radiant energy in accordance with the thermographic copying process. The contacting surface of the up-ended plain paper is promptly dusted with a colored developer powder of pigmented hard thermoplastic epoxy resin sphericles.,

The powder adheres at the areas corresponding to the pencilled lines of the drawing but not at the background areas, producing a replica of the original which is then briefly heated to fuse the resin and fix the copy. Up to 50 or 100 or more additional copies may be prepared from the drawing in the same manner, either immediately or after prolonged intermediate storage of the drawing either in a at le or rolled up into a tight roll. The pencilled drawing may be altered or removed and replaced; accurate copies of the corrected or substituted drawing are then produced by the same procedure.

Other hard-surfaced paper or thin dense paper-like sheet material may be used in place of the vellum, and the Santicizer 9 or other latent-image-producing material may be surface coated as described in the example, or may be incorporated in the paper in any desired manner, e.g. by application in molten form, or by impregnation from solution or dispersion, or during they forming of the paper, or by thermally induced transfer from another coated or impregnated sheet.

The coating weight of the Santicizer 9 or other latentimage-forming material may vary over a wide range. Too thick a coating may cause image blurring; excessively thin coatings may produce fewer than the desired number of copies. Effective transfer sheets have been produced with coatings of from .08 gram per sq. ft., obtained by swabbing lightly with a one percent solution of the sulfonamide material, to as high as 1.36 g./sq. ft. obtained by application of the material in liquid molten form with a squeeze roll applicator. The incorporation of minor amounts of inert powders, together with small proportions of polymeric binders, makes practical the application of still heavier coatings of volatilizable transfer material as will subsequently be shown. A preferred range of coating weights is about one-half to about one gram per square foot of the transfer material in the absence of additives, or up to about one and one-half grams per square foot in conjunction wtih about one-third of that amount of added powder and binder.

A graphic original such as an engineering drawing may itself be coated with the transfer material as in the foregoing example, or the coating may less desirably be supplied as a separate thin conformable coated or impregnated web which is placed in heat-conductive close contact with the back surface of the untreated original.

Example 3 A thin uniform coating of Santicizer 9 is applied to thin dense smooth-surfaced paper by the method described in Example 2. A Verifax matrix paper, having a light-sensitive coating of silver halide in gelatin and also containing dye-forming and developing ingredients, is placed over a graphic original and then exposed to light by reflex illumination. The exposed matrix is immersed in an activator solution which promotes developing, dye formation, and tanning or hardening of the gelatin at the exposed portitons. The unexposed areas become chemically fogged and the dye is formed, but the gelatin remains unhardened. The gelatin-coated sheet while still damp is pressed against the uncoated surface of the paper carrying the coating of Santicizer 9 and the sheet then stripped away. The unhardened or unexposed areas of the gelatin layer split, leaving residual colored infra-redabsorptive image areas corresponding to the colored image areas of the graphic original. The thus imaged master, after Idrying if necessary, is placed with the Santicizer 9 coating against a sheet of plain paper and the imaged surface is briefly exposed to intense radiation rich in infra-red, forming a latent image on the paper. The surface carrying the latent image is dusted with pigmented thermoplastic resinous developer powder, producing a replica of the original which is then rendered smudge-resistant by heating.

Example 4 A master sheet is prepared Iby coating a transparent thin Mylar oriented polyester film with a thin uniform rst layer of a ball-milled mixture of 40 parts by weight of light-sensitive indium oxide pow-der, 9 parts of Pliolite S-7 rubbery butadiene-styrene copolymer, 21 parts of toluene, and 30 parts of methyl ethyl ketone, drying, applying a thin uniform coating of benzil in acetone, and again drying. The sheet is exposed to an intense projected light image, e.g. from a microfilm slide projector, through the transparent backing until the light-struck areas of the indium oxide coating become selectively infra-red-absorptive. The sheet is then placed with its coated surface in contact with a sheet of plain paper and is briey exposed to intense radiation rich in infra-red as for the thermographic copying process. A latent image is formed on the paper sheet and is promptly developed by dusting the sheet with developer powder and fixed by brief heating. A sharp clean copy is obtained. After the initial sensitivity of the indium oxide layer is restored, e.g. by storage in absence of light, the process can be repeated using a different light-image. The master sheet is normally not receptive of developer powder and can be handled, shipped and stored without diiculty.

The eutectic mixture of 82 parts benzil and 18 parts benzoin is also useful as a master sheet coating.

Example 5 A suspension is prepared by ball-milling together ten parts by weight of silver behenate, Ve parts of phthalazinone, 3 parts of Parapol S-50 styreneisobutylene copolymer, and 85 parts of heptane. The mixture is coated on map overlay tracing paper using a coating knife at an orice of 11/2 mils. The coating is dried.

A second coating of a solution, in ten parts of methanol, of one part of ethyl cellulose, 0.04 part of 4-methoxy-l-naphthol, and 0.0043 part of erythrosin, is applied over the rst coating at Ian orifice of 2 mils and dried at room temperature in the dark.

The reverse surface of the sheet is lightly swabbed with a 20% solution of Santicizer 9 in acetone, and dried.

A graphic original, in this case printed in black ink on thin white paper, is placed with the unprinted surface in contact with the dyed surface of the coated master sheet and the composite is briefly intensely irradiated as in thermographic yback-printing. A blue-black infra-redabsorptive reproduction of the original printed image is produced on the master sheet. The copy is then irradiated for 45 seconds at 20,000 foot-candles with light from a ZOU-watt incandescent-filament projection lamp. No visible change occurs in the copy-sheet. The background areas are found to be stabilized against visible change on heating.

The copy-sheet is next placed with its coated reverse surface against a sheet of plain paper, the colored image is selectively heated by brief exposure of the sheet to intense infra-red radiation, and the resulting metastable latent image formed on the paper is promptly developed with thermoplastic colored resinous developer powder and fixed by heating. A large number of copies may thus be made. The copy-sheet may be stored with other papers for subsequent preparation of additional copies as needed, without deterioration of the copy-sheet or of papers placed in contact therewith.

The substitution for the plain paper of a direct image offset lithographie paper plate permits the preparation of any desired number of additional copies by lithographie duplication procedures. A thermally softenable resinous organophilic or ink-receptive developer powder is used; the powdered mixture of sulfonamide-forfmaldehyde resin, phenolic resin, and pigment 4described in Example 1 is l l' particularly useful for this purpose. It adheres to the metastable liquid latent image, is fused to the plate and into a smooth surface by brief heating, and is then selectively wet by the oily lithographic ink. The hydrophilic background areas of the direct image plate are selectively wet by the aqueous fountain solution.

In the foregoing example the master sheet is first heated at image areas to provide the radiation-absorptive image, and the background areas are then desensitized to prevent gradual spread of the image during continued subsequent irradiation and heating. The reverse procedure, of desensitizing the 'background areas by irradiation through the non-opaque background areas of an original followed by heating to develop the image areas, is equally useful.

The Sancticizer 9 or other latent-image-producing material may be incorporated directly in the image-forming layer, for example with the binder, reactant and dye of the surface coating in the foregoing example, to provide a master sheet from which reverse-reading developable latent images may be prepared by thermographic front-printing procedures.

Example `6 An intermediate master sheet is prepared by coating one surface of map overlay tracing paper with a silver dispersion as described in Example l. The reverse surface of the paper is coated with a solution of l parts by weight of Santicizer 9 and l0 parts of methyl gallate in 80 parts of acetone. The sheet is dried after each coating. A11 image is formed in the silver coating using a pre-exposed transfer sheet and employing the procedure described in Example 1. The sheet is placed with the coated reverse surface in contact with plain paper and subjected to brief` intense irradiation, forming a latent image on the paper.

The image is then made visible by dusting with a reactive o developer powder, removing loose powder, and heating. The powder is white in color and is darkened only when heated in the presence of the methyl gallate. Any slight residue of the powder remaining on the background areas of the copy therefore remains unchanged, so that the background areas remain completely free of color.

A preferred chemical developer powder useful in conjunction with the master sheet of this example consists of finely powdered silver behenate containing a small proportion of a toner, for example about 15% of phthalazinone. Other fusible silver soaps and other image toners are also effective. The addition of small amounts of inert powders such as silica powder is advantageous in preventing lumping of developer powders of this type.

AExample 7 A photoconductive copy-sheet having a coating of dyesensitized Photoconductive zinc oxide in an insulating binder is coated on the reverse surface with a thin coating of benzoin, applied from solution in acetone, to form a transfer master sheet. The zinc oxide coating is electrostatically charged, exposed to a light-image, and developed with electrostatic developer powder to produce an infra-redabsorptive image. The sheet is place-d with its reverse surface in contact with plain paper and the imaged surface is exposed to brief intense irradiation to form a latent image on the paper which is then dusted with thermoplastic colored developer powder and fixed by heating. The steps of forming the latent image and developing the visible image are repeated to a total of up to at least about 100 copies of excellent detail and contrast.

Example 8 Benzil in powder form is dusted over the back surface of a sheet of lightweight bond paper printed on the front surface with graphic indicia in black radiation-absorptive ink. The powder is brushed uniformly over the paper surface with a short-bristled paint brush and the excess removed by shaking. The sheet is placed with its coated surface in contact with a plain sheet of paper and the printed surface is briefly exposed to intense irradiation.

The second sheet is removed and the contacted surface dusted with colored fusible developer powder. A copy of the original is obtained and is xed by heating. A second copy is similarly obtained. Where additional copies are desired, application of the benzil must be repeated. The procedure is therefore particularly useful where but one or two copies are required. It is also applicable to repetitive processes wherein the original is mechanically repowdered and returned to exposure position after each exposure, in which case a rotary brush of Dacron polyester ber flock on-a revolving drum or cylinder provides an excellent means for applying the powder to the sheet surface. No substantial buildup of benzil or other latentl image-forming powder occurs at background areas of the original, the coating weight being and remaining well below one-half gram per square foot.

Similar image-transfer and -development steps may be carried out with imaged coated master sheets having other light-sensitive coatings employing other means for developing the latent image. Image masters prepared on lightsensitive silver-containing coated sheet materials as used for photographic printing-out papers or for photographic films are particularly effective because of the excellent absorptivity of the silver-containing image for infra-red radiation. Photoconductive zinc oxide coatings on which the light-struck image areas may be made visible by electrolytic developing means are also particularly useful because of the high reffectivity of the coated background. In all cases the image areas are selectively heated on irradiation to form on the plain paper receptor a metastably liquid, at least temporarily powder-retaining, latent image.

A mixture of benzil and bezoin has been mentioned in Example 4 as an effective master sheet coating; and mixtures of other fusible vaporizable solids which form metastable liquid condensates are also useful. Mixtures of one part of benzil with from about three to about six parts of Santicizer 9 have given particularly effective results. Other materials may be included in the transfer coating, the addition of inert powder such for example as silica powder being especially helpful in increasing the number of copies which may be obtained. Other useful inert powders include powdered glass or glass spheroids. With these materials may be incorporated small amounts of polymeric film-forming binders which aid in preventing loss of the coating by abrasion or flaking while still permitting vaporization and offsetting of vaporizable solid.

Example 9 The following components in the indicated Weight proportion are mixed together by milling in a ball mill.

Benzil 6.22 Santicizer 9 24.87 Polymethyl methacrylate (Lucite 44) 4.35 Silica powder (Syloid 244) 6.22 Acetone 75.74

The mixture is coated on l2 lb. Jupiter paper at a coating weight after drying of two grams per sq. ft. A sheet of the coated paper is printed on the reverse surface with a typewritten legend, producing a master sheet as illustrated in FIGURE 7. Copies are made on plain white paper from the master sheet by irradiation, powder development, and heat fixing as described in the previous examples. A total of 250 complete and fully readable copies is produced.

The copies are compared with those produced from masters having identical coatings except for the proportion of silica powder. Increasing the amount of silica powder to ten parts produces no observable difference; after 250 copies the images are fully developed and readable. At two parts of silica powder about good copies are produced. A master sheet containing no silica powder produces only about 50 good copies; at 150 copies the images are so faint and blurred as to be illegible.

By means of similar comparative tests it is shown that 13 the amount of polymethyl methacrylate may be varied from as low as about two parts to as high as about ten parts without any significant loss of image at up to 200 copies; whereas within this range and in absence of the silica powder only about 50 to 100 good copies are o'btained.

The particle size of the silica or other inert powder is not critical, equally favorable results being obtained with silica powders having nominal particle size of 2.9, 3.3, 7 and 1l microns.

Example 10 Example 11 Paper is coated on one surface with a mixture of two parts by weight of benzil, thirteen parts of Santicizer 9, four parts of Hysil 233 silica powder, and 81 parts of 2% ethyl cellulose in acetone, and dried. The sheet is then similarly coated on the other surface with a mixture of the following components Parts by weight Silver behenatezbehenic acid 12.6

Phthalazinone 5.2 2,6-ditertiarybutyl-4-methylphenol 2.2 Zinc oxide 50 Terpene resin (Piccolyte S-135) 10 Polyvinyl acetate 7.3 Cellulose acetate 12.5 Tetrachlorophthalic anhydride 0.2.

Acetone to make a spread-able mixture.

A transfer sheet as employed in Example 1 is exposed in contact with .a printed original and is then heated in contact with the silver soap coating to produce thereon an infra-red-absorptive copy of the original. The resulting master sheet is then employed to produce up to 250 good copies of the original on white paper, using the procedures previously described.

Copies made as herein described are characterized by wide latitude in reproduction of both narrow and wide print lines and other areas. As an example, letters typed on letterheads having wide inked borders or insignia are reproduced in full detail and without blurring of the typed message or hollowing or outlining of the wide areas.

What is claimed is as follows:

1. The method of making a copy of a graphic original having visibly different image and background areas comprising: placing a master sheet, having a stable transfer layer comprising from about one-half to about one and one-half grams/sq. ft. of hard non-tacky fusible solid material melting within the approximate range of 70 to 170 C. and vaporizable at 150 C. with formation of a fluid metastable liquid condensate which remains in liquid form for atleast about one-half minute on cooling to room temperature, with its transfer layer in close contact with the surface of a receptor body; locally briefly heating said master sheet in a pattern corresponding to the image areas of said original and to a temperature sufficient to cause transfer of said vaporizable material to said surface whereby to provide at corresponding image areas of said receptor body surface a metastable liquid latent image; and promptly applying over `said receptor surface a freely flowing image developer powder which is adherently held by said metastable liquid.

2. The method comprising: placing a master sheet, having on one surface a preferentially radiation-absorptive image pattern and having uniformly distributed over the other surface a layer of from about one-half to about one and one-half grams/sq. ft. of hard non-tacky fusible solid material melting within the range of approximately 7.0" C. to 170 C. and vaporizable at 150 C. with formation of a lluid metastable liquid condensate which -remains in liquid form for at least about one-half minute on cooling to room temperature, with its said other surface against 4the surface of a receptor sheet; briey exposing the imaged surface of said 'master sheet to said radiation at high intensity to cause heating at said image pattern and transfer to said receptor surface of said vaporizable material in a corresponding pattern to form a metastable liquid latent image; removing and cooling the receptor sheet; and promptly applying over the surface thereof a freely flowing image developer powder adherently retained by said metastable liquid for making visible the latent image.

3. The method comprising: imparting a preferentially radiation-absorptive image pattern to the surface of a master sheet having uniformly distributed over its other surface a layer of from about one-half to about one and one-half grams/sq. ft. of hard non-tacky fusible solid material melting within the range of approximately 70 C. to 170 C. and vaporizable at 150 C. with formation of a fluid metastable liquid condensate which remains in liquid form for at least about one-half minute on cooling to room temperature; placing said master sheet with its said other surface against the surface of a receptor sheet, and briefly exposing the imaged surface of said master sheet to said radiation at high intensity to cause heating at said image areas and transfer to said receptor sheet of said vaporizable material at corresponding areas to form a metastable liquid latent image; removing and cooling the receptor sheet; and promptly applying over the surface thereof a freely flowing image developer powder adherently retained by said metastable liquid for making visible the latent image.

4. The method comprising: placing in close contact with a receptor sheet the coated surface of a master sheet having a transfer coating of components comprising from about one-half to about one and one-half grams/sq. ft. of hard non-tacky fusible material melting within the approximate range of 70 to 170 C. and vaporizable at 150 C. with formation of a uid 'metastable liquid condensate which remains in liquid form for at least about one-half minute on cooling to room temperature, and a vaporizable first reactant; locally briefly heating said master sheet in a pattern corresponding to a desired visible image and to a temperature suflicient to cause transfer of vaporizable material from said master sheet to said receptor; applying over said receptor an essentially colorless free-owing fusible particulate developer material comprising a fusible second reactant which is rapidly inter-reactive at its fusion temperature with said first reactant with formation of a distinctively colored reaction product; removing any excess powder; and heating said receptor to develop a permanent visible image.

5. The method of claim 1 wherein said solid material is a material possessing a strong tendency to form a supercooled melt and selected from the class consisting of a mixture of oand p-toluene sulfonamides melting at about C., a solid chlorinated diphenyl having a vapor pressure of 760 mm. Hg at about 435 C., benzotriazole, 2,4-dihydroxy benzophenone, tribenzylamine, benzil, vanillin, benzoin, phthalophenone and mixtures thereof.

6. The method of making copies comprising the steps of: 1) placing a master sheet having on one surface a preferentially radiation-absorptive image pattern andv having uniformly distributed over the other surface a layer, comprising a blend of (a) from about one-half to about one and one-half grams/sq. ft. of hard non-tacky fusible solidmaterial melting within the range of approximately 70 C. to 170 C. and vaporizable -at 150 C. with formation of a uid metastable liquid condensate which remains in liquid form for at least about one-half minute on cooling to room temperature with minor proportions of (b) inert powder and (c) polymeric binder, with its said other surface against the surface of a receptor sheet; (2) briefly exposing the imaged surface of said master sheet to radiation at high intensity to cause heating at said image pattern and transfer to said receptor surface of said vaporizable material in a corresponding pattern to form a metastable liquid latent image; (3) removing the receptor sheet while permitting cooling thereof, 4and promptly applying over the receptor surface a freely flowing image developer powder adherently retained by said metastable liquid to produce a lirst copy; and repeating the several steps to produce additional copies.

7. The method of claim 6 wherein said solid material is a material possessing a strong tendency to form a supercooled melt and selected from the class consisting of a mixture of oand p-toluene sulfonamdes melting at about 105 C., a solid chlorinated diphenyl having a vapor pressure of 760 mm. Hg at about 435 C., benzotriazole, 2,4-dihydroxy benzophenone, tribenzylamine, benzil, vanillin, benzoin, phthalophenone and mixtures thereof.

8. The method of claim 6 including the preliminary step of imparting said preferentially radiation-absorptive image pattern to the master sheet.

9. The method of claim 8 wherein the image pattern is imparted by printing.

10. The method of claim 8 wherein the master sheet is provided over its said one surface with a coating comprising a irst reactant and the image pattern is imparted thereto by reaction at image areas with a second reactant, said iirst and second reactants being inter-reactive on heating together at 150 C. with formation of an infrared-absorptive reaction product.

11. The method of claim 8 wherein the master sheet is provided over its said one surface with a photosensitive coating and the image pattern is imparted thereto by a process including exposure to a light-image.

12. The method of claim 11 wherein the master sheet is provided over its said one surface with a photoconductive coating and the image is imparted thereto by diiferential deposition.

13, The method of claim 11 wherein the master sheet is provided over its said one surface With a photosensitive silver salt coating and the image is imparted thereto by reduction of silver ion at the light-exposed areas.

References Cited UNITED STATES PATENTS 2,955,052 l0/1960 Carlson et al 117-17.5 3,088,028 5/1963 Newman Z50-65.1 3,094,619 6/1963 Grant 250-65 3,108,896 10/1963 Owen 117-369 X 3,121,791 2/1964 Russel Z50- 615.1 3,146,348 8/1964 Workman 117-368 X 3,196,029 7/ 1965 Lind 1l71.7 3,207,602 9/1965 Shely 96-27 3,280,735` 10/1966 Clark et al Z50-65.1 X

FOREIGN PATENTS `60,431 2/ 1961 Republic of South Africa. 137,036 3/1961 U.S.S.R.

J. TRAVIS BROWN, Primary Examiner.

R. E. FIGHTER, Assistant Examiner.

U.S. Cl. X.R. 

